A large number of esters oxyacids of pentavalent phosphorus are produced as articles of commerce e.g. phosphates, thiophosphates and phosphonates. The majority of them are produced by the reaction of an alcohol or phenol with phosphorus oxychloride or with a chloridate. Such reactions are inherently disadvantageous in so far as they involve the handling of chlorine or a derivative thereof.
The present invention finds particular application to processes for the production of phosphate esters. Triaryl phosphates are produced in large quantities by the reaction of phenol or alkyl substituted phenols or a mixture of such phenols with phosphorus oxychloride. Monoalkyl diaryl phosphates are produced by the reaction of phosphorus oxychloride with one molar proportion of an alcohol and the subsequent reaction of the dichloridate produced with a phenate anion.
There have been proposals to produce mixed alkylaryl phosphate esters by the transesterification of a triaryl phosphate such as triphenyl phosphate with an aliphatic alcohol. Finley, U.S. Pat. No. 4,443,384, discloses carrying out such a transesterification by initially adding aqueous sodium hydroxide to the alcohol to form an alkoxide and subsequently reacting that alkoxide with the triaryl phosphate. Finley, U.S. Pat. No. 4,482,506, discloses carrying out such a transesterification in the presence of a phenoxide catalyst. The phenoxide is stated to function by virtue of interacting with the alcohol to generate an alkoxide and the reaction is effected by initially reacting the phenoxide with the alcohol and subsequently adding the triaryl phosphate. None of these proposals has been entirely successful in producing a high yield of alkyl aryl phosphate (i.e., a product containing only small amounts of unreacted triaryl phosphate) and all suffer from a tendency towards by-product formation and concomittant catalyst deactivation. The manufacture of phosphate esters has continued to be practised on a large scale using phosphorus oxychloride or a chloridate as a raw material despite the attendant disadvantages thereof.